How much does life need salt?
There’s nothing like a pinch of salt to elevate a bowl of popcorn to its ultimate moreish satisfaction. Our love for salt echoes back to our ancestral origins in the sea.
Whether the cradle of life on Earth was a warm little pond, as Darwin imagined, or an active hydrothermal vent, it was almost certainly an environment rich in sodium and chlorine atoms. Four billion years later, the biological processes that drive the machinery of life still depend on a precise balance of these atoms inside and outside the cell.
Minute changes in the concentration of sodium and chlorine atoms within our cells enable contractions of our heart muscles and the transmission of nerve impulses.
Egyptians used salt to preserve their mummies and salt remained a precious resource for the great empires that followed.
Geological records suggest that oceans on the young Earth may have been up to twice as saline as those of today, impeding global colonisation by the earliest microbes. It was only once plate tectonics kicked in, sequestering sodium and chloride-rich minerals into the mantle, that the concentration of sodium and chloride atoms decreased sufficiently to accommodate the proliferation of life in the oceans.
Although wet and salty environments are a likely feature of habitable planets, it’s not clear whether they would all be equally conducive to life. The early Martian seas may have been considerably more saline than seas on Earth and potentially more challenging for life that emerged on the red planet.
On Earth, fibres of biological cellulose have been found in microscopic pockets of water trapped within sodium chloride crystals dating back to almost 250 million years. Around 3 billion years ago, Mars lost most of its surface water through evaporation, turning once vast oceans into brines. So, if microbial life did indeed evolve in the Martian oceans, it could have fossilised within salt crystals that remain preserved on the surface.
Too soon for the crackers, however, as it will be some time before the first human explorers to Mars stumble on pickled aliens and bring them home for tea.